Work apparatus of this kind include a fuel tank wherein the fuel is stored for the operation of the internal combustion engine. Fuel is drawn by suction from the fuel tank by means of a fuel pump and is supplied to the carburetor of the engine in order to be there processed to an ignitable air/fuel mixture. For a clean mixture formation and a reliable running of the engine, it is necessary that the fuel be drawn free of bubbles. Otherwise, the mixture can become lean and, in the extreme case, this can lead to a stalling of the engine.
A lower-lying region of the fuel tank is selected wherein the fuel is drawn by suction referred to a usual work holding position which is constructively pregiven. In this way, the available fuel volume is at least approximately completely used before air is drawn. In portable work apparatus, during operation, angular positions, however, occur with reference to the gravitational direction (that is, the usual work position pregiven structurally) wherein a remaining component fill of fuel follows the weight force and collects in a side region of the fuel tank. In order to nonetheless make possible a bubble-free suction, a pendular-like suction unit is provided wherein a suction head is mounted at the end of the fuel line at the tank. The fuel line is configured in this region, for example, flexibly, so that the suction head can follow the fuel in the direction of the weight as a consequence of its own weight. Here, efforts are made to ensure that the suction head remains permanently immersed in the fuel as much as possible for different angular positions of the work apparatus in order to make possible an almost complete emptying of the fuel tank while simultaneously providing a bubble-free suction.
Limits are imposed with respect to the above-mentioned suction principle in the typical configuration of portable handheld work apparatus such as blower/suction apparatus, chain saws, brushcutters or the like which are provided for portable handheld operation. Here, there is the primary requirement for a small volume and lightweight configuration of such apparatus. The structural space available often compels construction wherein the fuel tank is configured comparatively wide transversely to the up direction and wherein the interior space of the fuel tank has numerous geometric irregularities. Although the suction head can lie on the base because of its own weight, for an inclined position, however, the suction head can move laterally only to a limited extent. The situation can occur that even a comparatively large remaining quantity of fuel collects so far laterally that the suction head can no longer follow the same and comes to rest above the level of the fuel. Air is then drawn by suction notwithstanding an adequate fuel quantity.
The typical design of portable handheld work apparatus is made difficult in that the fuel pump only has a low pumping capacity and that only low suction pressures are available. Even a short-term case of the suction head becoming dry can lead to the situation that the associated air induction leads to operational disturbances or even to stalling of the engine.